The B-57 is a modified version of the English Electric
Canberra which was first flown in Britain on May 13, 1949, and
later produced for the Royal Air Force (RAF). After the Korean
Conflict began in 1950, the USAF looked for a jet medium bomber
to replace the aging Douglas
B-26 Invader. In March 1951, the USAF contracted with the
Glenn L. Martin Co. to build the Canberra in the U.S. under a
licensing agreement with English Electric. The Martin-built B-57
made its first flight on July 20, 1953, and when production
ended in 1959, a total of 403 Canberras had been produced for
the USAF.

The only model of the Canberra now available is the WB-57
weather version, used by the National Aeronautics and Space
Administration. SEE: Canberra WB-57
- NASA